This invention relates to electronic oscillators and, more particularly, to lumped element microwave oscillators, that is, to oscillators comprising distinct electrical components whose physical dimensions are smaller than a wavelength. Specifically, the invention is directed to a lumped element microwave oscillator mounted on the back plate secured to a wave guide and to adjustably controlling the frequency and the power output of the oscillator.
The phenomenon that load variations can change both the frequency and the amplitude of electromagnetic waves generated by a microwave oscillator and transmitted by a wave guide is well known. In fact, various devices have been used in the past for varying the load in order to control the frequency and the amplitude of electromagnetic waves which propagate through a wave guide.
In cavity Gunn diode oscillators, adjustable capacitive tuning screws and inductive posts disposed in the oscillator cavity have been used for controlling the frequency of oscillation. However, lumped element microwave oscillators do not include frequency-determining cavities. Therefore, those types of adjustable capacitive tuning screws and inductive posts cannot be used.
Varactors have been used in lumped element microwave oscillators for controlling the frequency of oscillation as shown, for example, in Rubin, "Varactor-Tuned Millimeter-Wave MIC Oscillator," I.E.E.E. Transactions on Microwave Theory and Techniques, November, 1976, pages 866-867, Amoss et al., "A Multiband Lumped-Element Varactor-Tuned Gunn Oscillator," 1977 I.E.E.E. International Solid-State Circuits Conference, February, 1977, pages 122-123, and Cohen, "Varactor Tuned Gunn Oscillators With Wide Tuning Range For the 25 To 75 GHz Frequency Band," 1979 I.E.E.E. MTT-S International Microwave Symposium, Digest of Papers, May, 1979, pages 177-179. A varactor is a two-terminal solid-state device which exhibits a voltage-variable capacitance across a p-n junction, and the varactor capacitance can be adjusted by altering the applied voltage.
The use of varactors in a lumped element microwave oscillator provides control over a suitable, but narrow, range of frequencies. However, the applied voltage must be altered in order to adjust the varactor capacitance for controlling the oscillator frequency which is a disadvantage.
In the past, the power output of the oscillator has been controlled by adjusting the coupling between the oscillator and the load by means of various devices. Passive attenuators, such as resistive cards and irises, have been mounted in the wave guide for controlling the coupling between the oscillator and the load. In addition to the passive attenuators, active attenuators, such as pin diodes, mounted in the wave guide have also been used for controlling the coupling between the oscillator and the load.
The use of passive attenuators, such as resistive cards and irises, or active attenuators, such as pin diodes, has certain disadvantages. Provision must be made in the structure of the wave guide for the use of such devices which increases the cost of the wave guide. Furthermore, the passive attenuators must be carefully constructed and precisely oriented in the wave guide for controlling the coupling between the oscillator and the load. Adjustment of the orientation of a passive attenuator within a wave guide can be difficult. The use of an active attenuator, such as a pin diode, requires a dc source for biasing the diode which adds further expense.